Among sensors designed to detect biomolecules using an electrical signal, there is a TR-based biosensor having a transistor structure. The biosensor is manufactured through a semiconductor manufacturing process and has advantages in that the electrical signal is quickly converted and integration of ICs and MEMS is easy.
Detection of a biological reaction using a field-effect transistor (FET) is disclosed in U.S. Pat. No. 4,238,757 (1980). This patent relates to a biosensor for detecting proteins which detects an antigen-antibody reaction by measuring a current resulting from a change in a semiconductor inversion layer due to variation of surface charge concentration.
U.S. Pat. Nos. 5,466,348 and 6,203,981 disclose improvement of signal-to-noise ratio (S/N) using a thin-film transistor (TFT).
FIG. 1 is a cross-sectional view of a typical bio-FET according to the existing art. A source 112a and a drain 112b are formed on both sides of an n-type or p-type doped substrate 111. A gate 113 is formed on the substrate 111 to be in contact with the source and the drain. The gate 113 generally includes an oxide layer 114, a polysilicon layer 115 and a gate electrode layer 116, and probe biomolecules 117 are attached to the gate electrode layer 116. The probe biomolecules 117 are bound to target biomolecules via, e.g., hydrogen bonding. The binding between the probe biomolecules 117 and the target biomolecules is detected by measuring change in current via an electrical method.
However, the method described above is problematic in that charged biomolecules cannot be detected with reliable accuracy and reproducibility in an electrolyte solution 200.
And, the FET-based biosensor is disadvantageous in that the associated semiconductor manufacturing process is very complicated.